1. Field of the Invention
The invention relates to a remote control transmitter.
2. The Prior Art
Wireless remote control devices have long been used for remote control of movable objects such as cranes, locomotives, model airplanes, and toy cars. Such devices are also used with apparatus of the entertainment industry, especially apparatus with increased operating comfort, the different continuously variable adjustments such as sound intensity, contrast, color intensity, and brightness, and the adjustments variable in discrete steps such as the sender finder and the station selector, being changed through wireless remote control.
An ultrasonic signal is emitted from a transmitter which is changed in a receiver part into a corresponding control signal of the chosen frequency. Besides ultrasonic signals, infrared signals are also used for distant control. Different methods for the use of ultrasonic are already known.
The most simple method is that for each adjustment a special channel is assigned a frequency for characterizing the type of adjustment to be made. With continuously variable adjustments, two frequencies are usually necessary for the change of adjustment, one frequency for increasing and one for decreasing the adjustment. The amount of the desired change is fixed by different lengths of time of pushing of an input key. On the receiver side, for identification of the different frequencies, a number of resonant circuits corresponding to the number of frequencies is used, which makes necessary a time wasting calibration procedure before putting the receiver into service. In modern remote control systems which use integrated circuit networks, the arriving ultrasonic frequencies are converted into pulses, their repetition frequency being equal to the ultrasonic frequency. The pulses arriving within a determined time are counted in a counter and evaluated. Another known method is the Pulse-Code-Method. A coded pulse sequence is emitted by the transmitter and decoded in the receiver. This principle has the disadvantage that both the transmitter and the receiver are costly. Another disadvantage is the unsatisfactory freedom from interference, so misfunctions can occur especially at the maximum distance range or with weakened transmitting batteries.
With the use of ultrasonic signals there is the disadvantage that interferences in the transmitting path can occur, so the received ultrasonic oscillations do not correspond with the transmitted oscillations and so false operations are triggered. These interferences can result, for example, when the transmitted ultrasonic oscillation superpose with and are extinguished by ultrasonic oscillations reflecting in space.
Further, the ultrasonic-wave components of extraneous noises, such as key rattling, ringing of a telephone, or the sweep radiations of the horizontal line scan of a television receiver, or other interference sources such as ultrasonic washing plants or the simultaneous operation of several ultrasonic remote controllers, can produce a false operation. Expensive circuits and transmitting methods have been developed to prevent these false operations. A transmitting method is already known in which the elimination of interference is striven for with the use of two pulse-like reversible remote control signals. In this method, a first frequency is transmitted during the duration of pulse, as the desired frequency and, during the spacing pulses, a second frequency is transmitted as auxiliary frequency. The auxiliary frequency is transmitted until the receiver is not ready any more to receive or the amplitude of the auxiliary frequency transmitted is decreased so slowly that no more oscillations are produced which contain the desired frequency. The auxiliary frequency of the transmission oscillator is produced by a resonant circuit formed by a coil and a capacitor. Further, a pulse generator producing a pulse sequence is present which switches the auxiliary frequency on or off by means of an electronic switch. From this follows that the transmission oscillator oscillates during the duration of pulse with the desired frequency instead of with the auxiliary frequency. The number of pulses which are produced by the pulse generator depends upon which one of the keys connected with the pulse generator are operated. In this transmitting method it is disadvantageous that no further operating channel can lie between auxiliary and desired frequencies because the oscillation frequency at the frequency reversal covers the complete band lying between the auxiliary frequency and the desired frequency. Further, ultrasonic remote control with pulse modulation is known for televisions in which the ultrasonic signal consists of two chronological frequencies which are coded in their value in their respective duration. The frequency of the first ultrasonic tone determines the kind of information, such as whether a channel is chosen or a gain shall be changed, while the duration of the first ultrasonic tone fixes the channel number or, for example, the kind and direction of the gain change. Only the second ultrasonic tone releases the execution of the order stored previously. Its duration controls in digital steps the size of the gain change. The ultrasonic signal is amplified, limited, and filtered in the receiver and then changed into direct current signals. Through the ultrasonic signal, multivibrators are switched on or off which give up, during their duration of connection, pulses of exactly defined duration. These pulses are evaluated in decadic forward- and backward ring counters. Additional circuits are arranged at its outputs which pass on the digital orders directly or changed into analogue values to the stages to be controlled. It is disadvantageous with this remote control that the resonance effects make impossible an exact evaluation of the transmitted frequency packages. The circuit of the ultrasonic transmitter is still constructed of discrete electronic components.
Further, an ultrasonic transmitter is known which is constructed with a highly integrated circuit network which consists of an input keyboard, an integrated input code circuit, a resistance network, a matrix with coupling points, an integrated transmitter unit, and a pulse generator for producing an alternating chronological sequence of two pulses of a first and a second frequency, respectively. In order to enable transmission of several commands, altogether three integrated input coding circuits are switched in parallel respectively on five outputs. One of the input coding circuits serves for the production of a field first frequency, also called group frequency. This first frequency is produced independently of which key of the input keyboard is operated, and which variable second frequency, also called command frequency, is thereby produced. If one defines the gains as L and H, with parallel output circuits, the outputs which command level L are privileged. This means, that this circuit can give one clear first frequency as group frequency and this is the one which shows only L on the five outputs. This is disadvantageous if several frequencies are necessary, which is the case, for example, if plural receivers independent of each other shall be operated at the same time. This problem can be solved if each receiver is assigned its own group frequency. This is not possible with the known circuit.